C.—GEOLOGY. 95 
the available rainfall has in many instances been obtained by successful 
drilling, in spite of the complication of the question by surface pollution, 
and in the face of many legal inanities and much charlatanry. And 
the extension of these methods to arid regions, as in Australia and 
North Africa, has brought under cultivation large areas which needed 
nothing but the ‘ striking of the rock by the rod’ of the driller to make 
new oases in the desert, and thus render available some of the richest soils 
in the world. 
Much the same is true of overground supplies, which have been a bless- 
ing not merely in the towns and lands supplied, but to the rivers and 
drainage basins regularised and protected in large measure from ever- 
recurrent floods and the damage consequent upon them. Although in 
such works geological conditions are often taken into full account, an 
elaborate geological survey at a very early stage would in most cases more 
than pay its way. Such a survey would not only give a good preliminary 
idea of the nature and tectonics of the rocks underlying sites of dams 
and reservoirs, but it would save its cost in limiting the number and in 
giving rational direction to the inevitable pits which must be sunk, by 
restricting them to the elucidation of points which the surface mapping 
leaves obscure. It would at the same time direct attention to the 
innumerable pitfalls which sites often present and would generally provide 
on the spot much of the requisite material for construction. 
It is an arguable question whether the expenditure of such vast sums 
as have been devoted to the supply of large towns is entirely justified. 
The provision of a single supply of which large quantities are used for 
drinking, cooking, and industrial purposes, necessitates that the water 
shall be of immaculate purity, and this pure substance, the purest of all 
the things we consume, is employed—may we not say wasted ?—for 
flushing, washing, and a host of other purposes for which a less pure water 
would suffice. Surely the time has come when people could be educated 
up to the use of a dual supply, and this should be a commercial possibility 
where the area served and quantity used are really large. The experience 
of London has shown the very high cost of a single supply to all consumers 
and for all purposes, and the limits of future supply are almost in sight. 
7 It seems to be time that the problems of a dual service should engage 
geerious attention. 
_ Power.—Owing to the configuration and rainfall of the British Isles, 
and their congested population, we are apt to think of water questions in 
terms of supply, and, though we are using a certain amount of water for 
power, there is only a limited development possible. In many other parts 
of the Empire, however, this is becoming a valuable asset, and nowhere 
more than in Canuda, which is rapidly developing its resources on a very 
large scale. What has been said with reference to water-supply is of 
equal application here, for the physiographic conditions which bring about 
steep gradients, accompanied by large bodies of water, introduce factors 
of denudation, transport, and deposition by the water which call for most 
careful selection of sites for reservoirs and works, if the all too frequent 
disasters are to be avoided, and if the schemes are not to be ephemeral in 
duration and excessively costly in upkeep. 
With sources of power other than coal and water—including that 
_ of the tides—the geologist has little concern. But there has been brought 
